1. Field of the Invention
The present invention relates to an electroluminescent element used for illumination of a display unit, a controlling unit or the like of various electronic devices.
2. Background Art
Recently, in various electronic devices, and particularly portable terminal devices such as portable telephones, an electroluminescent element (EL element) emits light by using a small IC-drive inverter or the like so that a display unit such as an LCD or a controlling unit such as a push button is illuminated for recognition or operation in a dark place.
According to the conventional EL element, a shield plate is formed at the EL element itself or between the EL element and a circuit of an electronic device, and connected with a ground terminal to prevent electromagnetic noise which is generated from the inverter or the like and causes incorrect operation of the device (for example, see Japanese Patent Unexamined Publication H09-283278).
The conventional EL element is described hereinafter with reference to FIG. 6.
FIG. 6 is a sectional perspective view of the conventional EL element. Various layers are deposited on an upper surface of a light-transmitting substrate 1 such as a film so as to form the EL element. In FIG. 6, a light-transmitting electrode layer 4 made of indium-tin oxide (referred to as “In-Tin Oxide” or “ITO”) or the like is formed on the upper surface of substrate 1 by using a sputtering method, an electron beam method or the like. A bus electrode 2 is formed on the upper surface of substrate 1 so as to be connected with light-transmitting electrode layer 4, and an electrode terminal 2A extends from bus electrode 2 to a tail portion 3 of substrate 1.
A light emitting layer 5, a dielectric layer 6 and a backside electrode layer 7 are printed on light-transmitting electrode layer 4 in this order sequentially, and are covered with an insulating layer 8. Phosphors such as zinc sulfide (ZnS) or the like, which are base materials of luminousness, are dispersed in synthetic resin, thereby forming light emitting layer 5. Ferroelectric materials such as barium titanate (TiBa3) or the like are dispersed in synthetic resin, thereby forming dielectric layer 6. Backside electrode layer 7 is formed of an electric conductor such as silver or carbon resin.
In addition, a shielding layer 9 made of an electrical conductor such as silver or carbon resin is printed on insulating layer 8. An electrode terminal 7A of backside electrode layer 7 and an electrode terminal 9A of shielding layer 9 extend to tail portion 3, so that the EL element is constructed.
The EL element discussed above is intended to be placed at the back of an LCD, a push button or the like, and mounted to an electronic device. Electrode terminal 2A of bus electrode 2, electrode terminal 7A and electrode terminal 9A, all of which are formed on tail portion 3, are connected with the IC-drive inverter (not shown) or the like of an electronic circuit provided for the electronic device by using a connector or the like.
AC voltage is supplied from the inverter or the like at the electronic device, and applied via electrode terminal 2A and electrode terminal 7A to light-transmitting electrode layer 4, which is connected to bus electrode 2, and backside electrode layer 7. Then phosphors in light emitting layer 5 emit light and illuminate the display unit or the controlling unit of the electronic device from its back, so that the display unit or the controlling unit can be recognized even in a dark place.
Electrode terminal 9A is constructed to prevent electromagnetic noise generated from the inverter or the like for driving the EL element by using shielding layer 9 which is connected with the ground terminal of the electronic device, so that incorrect operation of the electronic device is prevented.
However, according to the conventional EL element, three electrode terminals (i.e., electrode terminal 2A, electrode terminal 7A and electrode terminal 9A) have to be connected with the electronic circuit of the electronic device, where electrode terminal 2A is connected with bus electrode 2 and light-transmitting electrode layer 4, electrode terminal 7A is connected with backside electrode layer 7 and electrode terminal 9A is connected with shielding layer 9. Therefore, tail portion 3 to which these three electrode terminals extend becomes large and a large connector for connecting therewith is required.
The present invention is directed to provide an EL element which is capable of reducing a size of the tail portion and which can be easily connected with the electronic device.